1. Field of the Invention
This invention relates to means for locating an ultra-precision position of a table particularly for a mask pattern exposure.
2. Prior Art
In recent years, techniques for producing integrated circuits are being developed with a rapid speed. Among others, a mask pattern exposure device by reduced projection, an electronic linear describer or the like is used, in which a X-Y moving table is an essential means for feeding wafers intermittently. The accuracy and moving time for locating the position of such X-Y moving table become indispensable factors for throughput of the device itself.
Conventionally, there is for example a X-Y moving means (shown in FIG. 1A), on which a table for minute moving exclusively is mounted, and its precise positioning is made by a piezoelectric element actuator. Such X-Y moving means is disclosed in the Scientific Symposium of the 1983 Spring Convention of Japan Society of Precision Engineering, and was manufactured as a test device by the Central Laboratory of Hitachi, Ltd. of Japan.
The aforesaid X-Y moving means comprises a double X-Y moving table 1 of a sliding guide construction and a pair of driving means 2 fixed on a base 3, the pair of driving means 2 being arranged on a X-axis and a Y-axis respectively.
The moving table 1 comprises a X-Y roughly moving table 4 (120 mm.times.120 mm) for a rough positioning of 5 .mu.m accuracy and a minutely moving table 5 mounted on the roughly moving table 4. A lower end of a cross-type X moving member 6 is guided by a X-axis guide groove 7 recessed in a center portion of the base 3, while an upper end thereof is connected to a Y-axis guide member 8, and the latter is moved in a X-axis direction. The X-Y roughly moving table 4 is mounted upon the X moving member 6, and moved slidably in both a X and Y directions on an upper surface of the base 3, while being supported by the guide member 8 as well as by four PTFE (polytetrafluoroethylene) sliding members 9 (containing glass fibers) disposed at four corners. For example, the PTFE commercially called "RULON A" may be used. All sliding portions are bonded by a PTFE sheet (not illustrated).
The minutely moving table 5 is supported on the roughly moving table 4 by four resilient bars 10 each having arcuately cutaway portion 10a at both ends, and driven by three cylindrical piezoelectric element actuators 11 incorporated between the both tables 4 and 5. Each piezoelectric element actuator 11 has a circulately cutaway resilient and deformable element 11a or an output terminal at its both ends. Under an application of 600 V, the piezoelectric element actuator 11 shows displacement of 18 .mu.m. Sealed in a gap of 100 .mu.m between the both tables 4 and 5 is a high viscosity silicone oil 12, thereby a damping function is available.
FIG. 2 shows a plane arrangement of the three piezoelectric element actuators 11.sub.x, 11.sub.y1 and 11.sub.y2. By varying the length of each piezoelectric element actuator, the minutely moving table 5 is moved in each direction of XY.theta., and the minutely moving table 5 indicates a displacement 13 as shown by moved values .DELTA.x, .DELTA.y, and .DELTA..sub.y2. Since each piezoelectric element actuator is, at its respective end, provided with the resilient and deformable output terminal 11a which is a rotating point, it has a parallel moving and sliding function. The maximum movable range of the minutely moving table 5 is .+-.8 .mu.m in both X and Y directions, and its .theta. rotation is .+-.160 .mu. rad.
Each driving means 2 comprises a DC servo motor 21 (hereinafter called "Motor") and a ball screw shaft 22. The driving means 2 disposed in a X-axis direction is connected to the X moving member 6, while the other driving means disposed in a Y-axis direction comprises further a Y-axis driving member 25 to be guided linearly by a roller guide 24. The Y-axis driving member 25 is linked with the minutely moving table 5 by way of a pair of rollers 26, 26, between which a rail 25a is disposed.
The positioning control of the roughly moving table 4 as well as of the minutely moving table 5 is made in a closed loop form by a laser interferometer (not illustrated), and there is adopted a dual mode control system for switching a speed control and a position control in accordance with a position deflection from a target value.
The X moving member 6 is moved with a high speed of 100 mm per second after starting. After a smooth speed reduction has been made along with a suitable speed reduction curve, a linear position control is carried out. The table speed signal is outputted by a tachogenerator 27 directly connected to the motor shaft, and switching of the control mode is made by selecting a suitable gain constant of the speed signals and of the position deflection signal.
On a Y-axis where a back-lash exists, after the motor speed has been reduced smoothly, the tachogenerator is run with a constant speed of 1 mm per second, and a pulse inverting signal is applied to the motor 21 at a distance of 1 .mu.m before the target value. Thus, as soon as the table stops movement, a back-lash of about 30 .mu.m is prepared.
Although the position control of the minutely moving table 5 is initiated at the time when the rough positioning has been ended, its yawing control is constantly corrected by the DC servo motor 21.
However, on the X-Y moving table 1 the Y roughly moving table and the X minutely moving table are separated from each other, so that a suitable parallel degree and a suitable right angle degree toward a mutual movement of each table are not given easily. Further, when the minutely moving table 5 is placed on the X-Y roughly moving table 4, the former may be affected by pitching, yawing or the like of the latter that is disposed immediately under the former.
As shown in FIGS. 1A and 1B, the tables 4 and 5 are supported by the four resilient bars 10. If the resilience of each bar 10 is not constant, the upper table 5 may be inclined.
As shown in FIG. 1B, each piezoelectric element actuator is mounted between the both tables 4, 5 fixed with each other, and one end of the piezoelectric element actuator is supported rotatably by the table 4, while the other end thereof is supported rotatably by the table 5. In this case, there is the danger that hysteresis may arise by friction resistance.
There is also known a device in which a X-Y moving table is moved by only piezoelectric element actuators. However, its movable range is extremely limited, and a high speed movement of the table is difficult.